This invention relates generally to video switching systems and, more particularly, to a video switching system adapted for use in a studio or program control room of a television broadcasting or recording station.
It is customary in the television broadcast and recording field to employ a plurality of separate pick-up cameras which view a scene to be televised or recorded from different angles or which view different scenes to be televised or recorded simultaneously as a composite picture. The cameras generate video signals corresponding to the respective scenes being viewed and these signals are typically routed to a video switching system which enables a program director to select the scenes to be presented for broadcasting or recording during the course of the program. Most such video switching systems also incorporate some sort of special effects generator which allows the program director to combine two or more video scenes in a variety of ways and to present the combined scenes to program to produce a variety of pleasing and interesting visual effects. Typical of the special effects generated by such systems are what are commonly referred to as effects and mixes. Effects allow the program director to split the screen, place inserts of various shapes and sizes therein, and generally wipe from one scene to another. Mixes allow the director to combine scenes so that both are visible on the same portion of the viewer's screen for a period of time and to fade a first scene out of while fading a second, new scene into the screen.
Many of the more elaborate and expensive studios include a separate television monitor for each camera being used as well as for the actual program so that the program director can continuously view each scene and make decisions as to which of the scenes require adjustment or editing and which are best suited for presentation to program. However, for reasons of economy and convenience, many studios, particularly smaller studios, are now equipped only with a single television monitor for previewing purposes. The video switching systems used in such studios generally include a set of controls that enable the individual selection of the scene or combination of scenes to be displayed on the preview monitor for inspection and a corresponding set of controls that enable the individual selection of the scenes for programming.
In a typical prior art video switching system of the above-described type, the preview selection controls are in the form of a group of switches, in most cases of the pushbutton variety and arranged in a row, with a separate such switch for each camera or other video signal source and perhaps additional such switches for initiating the preview of scene combinations (i.e., effects and mixes). The program selection controls take the form of an identical row and number of switches, positioned near, and usually directly beneath, the corresponding preview switches.
By depressing the switch in the preview group corresponding to a particular camera, the program director can have the scene being viewed by that camera displayed on the preview monitor for his inspection. If it is determined that the previewed scene is suitable for programming, the director depresses the corresponding switch in the program group and the program scene changes accordingly.
Prior video switching systems of the above type have some recognized drawbacks. For example, because there is a separate switch for each camera in the program selection group, it is readily possible for the program director to select any scene for broadcasting without first previewing that scene. This presents the possibility that scenes that are undesirable for one reason or another will be switched directly to program, whether inadvertently or in an effort to save time, without the benefit of editing or adjustment by the director.
Another drawback of prior video switching systems of the above type relates to the manner in which program changes take place. Specifically, when a program change is initiated by the depression of a program selection switch, the scene displayed on program switches abruptly and discontinuously from the old scene to the new scene. The abrupt switching from one scene to another under many circumstances gives an unpleasant and disagreeable impression to the program viewer. Additionally, it is desirable in some situations to fade the old scene out of the picture while the new scene is faded into the picture so as to give the impression of a gradual transition. In order for this to be accomplished with prior video switching apparatus, the program director must first generate a mix of the old and the new scenes, adjust the mix so that the old scene predominates, switch the mix to the program, then gradually adjust the mix so that the old scene is faded out and the new scene is faded in. To achieve this gradual changeover, the director must typically operate a pair of manual controls that selectively attenuate the video signals corresponding to the two scenes. The rate of the transition from one scene to the other is dependent upon the rate at which the controls are manipulated by the operator. Thus, it is extremely difficult to effect the transition at a uniform rate. Additionally, after the transition between the scenes is completed, the program monitor will display only the new scene even though the signal being presented to program is actually a mixture of the old and the new scene. The program director can easily forget that the mixture is present and, by moving the mix controls, inadvertently re-introduce the old scene into the program. To avoid this, the director must switch the program from the mixture and to the new scene alone prior to preparing for future program changes.
It is, therefore, a broad object of this invention to provide an improved video switching system.
Another object of the invention is to provide an improved video switching system that is particularly adapted for use in a small studio environment that includes only a single preview monitor and a single program monitor.
Another object of the invention is to provide an improved video switching system of the type described that is adapted to force a program director to preview each video scene on a preview monitor prior to selecting that scene for program.
Another object of the invention is to provide an improved video switching system that, after the initiation of a program change, automatically fades the old scene out and the new scene into the program without the need for first establishing a mix between the scenes and without the need for manipulating any manual controls.
Another object of the invention is to provide an improved video switching system of the type described in which the rate at which the transition from the old scene to new scene takes place can be selected anywhere within a relatively wide range of rates prior to initiating the change.
Still another object of the invention is to provide an improved video switching system of the type described that upon completing the transition from the old scene to new scene, automatically, abruptly and essentially invisibly switches the new scene alone to program so as to avoid the inadvertent re-introduction of the old scene into the program.